HDR File Format (.hdr)

An HDR file stores a high-dynamic-range raster image using Radiance's RGBE encoding, which packs red, green and blue mantissas with one shared exponent per pixel so a scene can hold a far wider range of brightness than a standard 8-bit image.

.hdrImage Files

HDR at a glance#

Full name	Radiance RGBE image format
File extension	.hdr
Category	Image Files
Developer	Greg Ward (Gregory Ward Larson)
MIME types	image/vnd.radiance
Other extensions	.rgbe.xyze
Compression	Lossless
Specification	Radiance picture file format
FileFlip support	FileFlip reads and writes this format

What a .hdr file can hold#

These are the things a HDR file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.

Lossless compression	Yes
High dynamic range	Yes

Strengths and limitations of HDR#

What HDR does well

Packs roughly the dynamic range of a 32-bit float image into 32 bits per pixel
Small enough that HDRI environment maps stay a manageable download
The reference decoder is simple and public, so most render engines implement it directly

Where HDR falls short

8-bit mantissa per channel gives less precision than a true floating-point format like OpenEXR
No alpha channel, so it cannot carry transparency or a matte alongside the image
One image per file, with no support for the extra render passes OpenEXR can bundle in

Reach for HDR when you need a compact high-dynamic-range environment map or lighting reference that most 3D tools and renderers can read without a plugin.

Convert HDR to OpenEXR when a VFX pipeline needs true floating-point precision, an alpha channel or multiple layers in one file, or convert it to JPEG or PNG once the image has been tone-mapped for a normal display.

How to open a .hdr file#

A .hdr file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts HDR into a format your machine already opens, and it does it in the browser tab rather than on a server.

Platform	Programs that open it
Windows	Adobe Photoshop, Luminance HDR, ImageMagick
macOS	Adobe Photoshop, Luminance HDR, ImageMagick
Linux	Blender, GIMP, Luminance HDR, ImageMagick
Web	FileFlip

HDR questions people ask#

What is an HDR file used for?

An HDR file most often stores an environment map or lighting reference for 3D rendering, since Radiance's RGBE encoding was built for the Radiance lighting-simulation software. Photographers also use the .hdr extension for panoramas merged from several exposures, before tone-mapping the result down to a normal image.

Is an HDR file the same as an iPhone or camera 'HDR photo'?

No. A phone's HDR mode blends several exposures and saves an ordinary JPEG or HEIC, while an HDR file with the .hdr extension is a Radiance RGBE file that keeps the full brightness range rather than compressing it into 8 bits. The two share a name but not a file format.

What's the difference between HDR and OpenEXR?

HDR (Radiance RGBE) packs each pixel into 32 bits with an 8-bit mantissa per channel and a shared exponent, while OpenEXR stores true 16- or 32-bit floating-point values per channel, supports an alpha channel, and can hold multiple image layers in one file. OpenEXR has mostly replaced HDR in VFX compositing, though HDR remains common for HDRI environment maps because of its smaller size and long-standing tool support.

Converting HDR files#

Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.